The invention relates more particularly to a dressing or finishing coating formed in situ on a molded article, that is to say inside its mold before separating the elements of the mold and extracting the article therefrom. Such a method for forming a coating is described in U.S. Pat. No. 4,668,460. A high pressure (several hundreds of bar) is necessary for sending the material of the coating between the mold and the article and ensuring a regular distribution of the coating on the surface of the article. The material enters the mold via a cylindrical chamber in which slides a rod forming an obstructor. When the rod is retracted, the chamber communicates with an injection circuit comprising pumps delivering the material at the desired high pressure. One drawback of this technique is that, short of limiting the pressures which can be used, it is necessary to give the chamber and the injection circuit a very robust structure which is therefore expensive.
U.S. Pat. No. 4,668,460 indicates that the above technique can be used for applying a coating material consisting of a mixture of two or more reactive components. The previously mixed components are injected via the same injection circuit. However, in order to save time when carrying out the method and therefore improving the productivity of the equipment, it would be desirable to be able to mix the components at the same time as the injection.
Another technique is indeed known in which a mixing head emerges directly towards the inside of the mold in order to mix and inject the components simultaneously. The head must, however, necessarily comprise orifices of small cross section in order to guarantee intimate mixing of the components, which limits the pressures which can be used in practice. Furthermore, this second technique requires division of the injection circuit delivering the high pressure.